Zhengcai Fu

Bio: Zhengcai Fu is an academic researcher from Shanghai Jiao Tong University. The author has contributed to research in topics: Lightning & Lightning arrester. The author has an hindex of 6, co-authored 34 publications receiving 580 citations.

Joint Optimization for Power Loss Reduction in Distribution Systems

Abstract: In distribution systems, network reconfiguration and capacitor control, generally, are used to reduce real power losses and to improve voltage profiles. Since both capacitor control and network reconfiguration belong to the complicated combinatorial optimization problems, it is hard to combine them efficiently for better optimization results. In this paper, a joint optimization algorithm of combining network reconfiguration and capacitor control is proposed for loss reduction in distribution systems. To achieve high performance and high efficiency of the proposed algorithm, an improved adaptive genetic algorithm (IAGA) is developed to optimize capacitor switching, and a simplified branch exchange algorithm is developed to find the optimal network structure for each genetic instance at each iteration of capacitor optimization algorithm. The solution algorithm has been implemented into a software package and tested on a 119-bus distribution system with very promising results.

MOV Failure Modes and Microstructural Characteristics Under Operating Duty Tests With Multiwaveform Multipulse Currents

Abstract: Low-voltage (LV) metal oxide varistor (MOV) is the main voltage limiting element employed in surge protective devices to protect sensitive equipment against lightning currents. MOV failures may threaten the security of electrical and electronic systems. In order to investigate the MOV failure modes under lightning strokes more realistically, operating duty tests with multiwaveform multipulse currents (indicated as “MODT”) are carried out on LV MOVs under simulated operating circumstances. To understand the mechanisms of MOV failure, microstructural examinations, including the elemental composition and phase constituent, are conducted on the tested samples with different failure modes. Experimental results show that the main failure modes for LV MOVs under MODT include coating crack, puncture, and cracking. The multiwaveform multipulse currents with larger amplitudes, shorter interpulse time, as well as when the subsequent steep currents occur before the intermediate stroke current, will result in more serious degradation on MOVs. The microstructural examinations on punctured MOVs show that the white intergranular layers become thicker, and the intergranular phase coats the zinc oxide (ZnO) grains. In addition, the decrease of ZnO grain size is observed both on the punctured and fractured MOV surfaces. Based on these microstructural characteristics, the mechanisms of different MOV failure modes are discussed.

Analytical Expressions for DG Allocation in Primary Distribution Networks

Abstract: This paper proposes analytical expressions for finding optimal size and power factor of four types of distributed generation (DG) units. DG units are sized to achieve the highest loss reduction in distribution networks. The proposed analytical expressions are based on an improvement to the method that was limited to DG type, which is capable of delivering real power only. Three other types, e.g., DG capable of delivering both real and reactive power, DG capable of delivering real power and absorbing reactive power, and DG capable of delivering reactive power only, can also be identified with their optimal size and location using the proposed method. The method has been tested in three test distribution systems with varying size and complexity and validated using exhaustive method. Results show that the proposed method requires less computation, but can lead optimal solution as verified by the exhaustive load flow method.

Imposing Radiality Constraints in Distribution System Optimization Problems

Abstract: Distribution systems commonly operate with a radial topology, so all models of optimization problems in these distribution systems should consider radiality in their formulation. This work presents a literature review, a critical analysis, and a proposal for incorporating the radiality constraints in mathematical models of optimization problems for radial distribution systems. The objective is to show that the radiality constraints on such optimization problems can be considered in a simple and efficient way. The reconfiguration and expansion planning problems of distribution systems are used to test and verify the proposed radiality constraints. A generalization of radiality constraints is also examined.

Optimal Network Reconfiguration of Large-Scale Distribution System Using Harmony Search Algorithm

Abstract: Electrical distribution network reconfiguration is a complex combinatorial optimization process aimed at finding a radial operating structure that minimizes the system power loss while satisfying operating constraints. In this paper, a harmony search algorithm (HSA) is proposed to solve the network reconfiguration problem to get optimal switching combination in the network which results in minimum loss. The HSA is a recently developed algorithm which is conceptualized using the musical process of searching for a perfect state of harmony. It uses a stochastic random search instead of a gradient search which eliminates the need for derivative information. Simulations are carried out on 33- and 119-bus systems in order to validate the proposed algorithm. The results are compared with other approaches available in the literature. It is observed that the proposed method performed well compared to the other methods in terms of the quality of solution.